1. Understanding the quantum threat
Quantum computing
Computing that uses quantum physics to perform calculations. Quantum computers could outperform conventional computers on certain tasks, including some mathematical problems underlying today’s cryptography.
Qubit
The basic unit of quantum information. Unlike a conventional bit, a qubit can be prepared in a superposition of its two basis states.
Physical qubit
An individual quantum component in a machine. Physical qubits are susceptible to noise and errors.
Logical qubit
An error-corrected unit of quantum information encoded across physical qubits. Physical and logical qubit counts are different measures of a quantum computer’s capabilities.
Quantum error correction
Techniques for detecting and correcting errors in quantum information. Reliable cryptographic attacks would require substantial advances in error correction and hardware.
Cryptographically relevant quantum computer (CRQC)
A quantum computer powerful and reliable enough to threaten widely used cryptographic systems. A quantum computer’s existence alone does not mean it can break cryptography.
Shor’s algorithm
A quantum algorithm that could break cryptographic systems based on integer factorization or discrete logarithms, including RSA and elliptic-curve cryptography, when run on sufficiently capable hardware.
Grover’s algorithm
A quantum algorithm that speeds up unstructured search. It affects the security margins of symmetric cryptography and hash functions differently from Shor’s attack on public-key cryptography.
Q-Day
An informal name for the point when quantum computers can break important cryptographic protections. It is not a confirmed date or a universally defined milestone, but some recent estimates predict Q-Day as early as 2029.
Harvest now, decrypt later (HNDL)
An attack strategy in which adversaries collect encrypted information today to decrypt it using future capabilities. This concerns confidentiality; blockchain signature forgery is a separate quantum risk.
Harvest now, forge later
A post-quantum threat model in which attackers preserve signed data, software, or transaction records today with the goal of using future quantum capabilities to forge signatures and undermine the systems that establish digital trust — including code signing, software update channels, identity systems, and blockchain consensus.
At-rest attack
In quantum blockchain research, an attack against assets whose vulnerable public keys are already exposed, without needing to wait for a new transaction.
On-spend attack
An attack that targets a public key exposed during spending and attempts to forge a competing transaction before the legitimate transaction is confirmed. Applicability depends on the blockchain’s design.
2. Understanding the technology
Cryptography
Mathematical techniques used to protect information, verify authenticity, and detect unauthorized changes.
Encryption
Converting readable information into ciphertext to protect its confidentiality. Encryption and digital signatures serve different purposes.
Public-key cryptography
Cryptography using a related pair of keys: a public key that can be shared and a private key that must remain secret.
Public key
A key that others can use to verify signatures or, in suitable encryption systems, encrypt information for its owner.
Private key
A secret key used to create signatures or perform other cryptographic operations. Its function depends on the algorithm.
Post-quantum cryptography (PQC)
Cryptographic algorithms designed to resist attacks from both conventional and quantum computers. They operate on conventional hardware.
Quantum-resistant / quantum-resilient
Descriptions of cryptography designed to withstand known quantum attacks. These terms identify the specific protections involved, rather than imply an unconditional security guarantee.
Lattice-based cryptography
Cryptography based on mathematical problems involving lattices: structured arrangements of points in multiple dimensions. Falcon and several other post-quantum algorithms use lattice-based constructions.
Hash-based signatures
Digital signature schemes built primarily from cryptographic hash functions. They offer an alternative to lattice-based signatures.
Quantum cryptography
Security techniques that use quantum physics directly, such as quantum key distribution. This differs from post-quantum cryptography, which uses mathematical algorithms on conventional computers.
Key encapsulation mechanism (KEM)
A cryptographic mechanism for establishing a shared secret over a public channel. That secret can then support encrypted communication.
ML-KEM
A post-quantum key encapsulation mechanism standardized in NIST FIPS 203 and derived from CRYSTALS-Kyber. It establishes shared secrets; it does not sign blockchain transactions.
ML-DSA
A lattice-based digital signature algorithm standardized in NIST FIPS 204 and derived from CRYSTALS-Dilithium.
SLH-DSA
A hash-based digital signature algorithm standardized in NIST FIPS 205 and derived from SPHINCS+.
Falcon / FN-DSA
Falcon is a post-quantum digital signature algorithm that uses lattice-based cryptography to create quantum-resistant digital signatures. Selected by NIST for standardization, Falcon is designed to combine strong post-quantum security with compact keys and signatures, making it well suited for systems where efficiency and data size matter. It is the first PQ algorithm that Algorand implemented.
FN-DSA is NIST’s standardized form of the Falcon post-quantum digital signature algorithm. It uses NTRU lattice-based cryptography to create quantum-resistant signatures with compact public keys and signatures, helping secure digital systems against future quantum attacks.
3. Understanding blockchain protection
Digital signature
Cryptographic evidence that a message or transaction was authorized by the holder of a signing key and has not been altered. A signature does not hide the transaction’s contents.
Elliptic-curve cryptography (ECC)
Public-key cryptography based on mathematical problems involving elliptic curves. A sufficiently capable quantum computer could undermine these problems using Shor’s algorithm.
ECDSA
The Elliptic Curve Digital Signature Algorithm. Used by several major blockchains, it is vulnerable to sufficiently powerful quantum attacks.
Ed25519
An elliptic-curve digital signature scheme used by traditional Algorand accounts. Like other elliptic-curve signature schemes, it is vulnerable to sufficiently capable quantum computers.
Cryptographic hash function
A function that maps input data to a fixed-length output, or digest. Blockchains use hashes for functions such as linking blocks and checking data integrity. Hashes are distinct from signatures.
Transaction authorization
The rules and cryptographic evidence determining whether an account permits a transaction. Post-quantum signatures can strengthen this layer without upgrading every other part of a blockchain.
Consensus security
Protection of the process through which network participants agree on valid blocks and transactions. Its cryptographic requirements extend beyond individual account signatures.
Historical-state verification
Checking evidence about a blockchain’s past state. Protecting historical attestations is a different function from protecting current account spending or consensus.
Post-quantum multisignature (multisig)
An authorization arrangement requiring multiple approvals and incorporating post-quantum signatures. Its protection depends on the algorithms and approval policy.
Hybrid signatures
An arrangement combining classical and post-quantum signatures. Whether both signatures are required, or either is accepted, materially affects the protection provided.
End-to-end quantum resilience
A system-wide objective covering relevant accounts, consensus, applications, custody, and supporting infrastructure. Deploying one post-quantum feature does not establish protection across all these layers.
4. Preparing for migration
Post-quantum migration
The process of moving from quantum-vulnerable cryptography to post-quantum alternatives. It includes discovery, planning, implementation, compatibility testing, and deployment.
Cryptographic inventory
A record of the algorithms, keys, certificates, protocols, and cryptographic dependencies used across an organization’s systems.
Cryptographic discovery
The process of identifying where cryptography is used, including in software, hardware, services, and third-party dependencies.
Migration roadmap
A staged plan explaining what will change, in what order, who is responsible, and which dependencies must be resolved.
Interoperability
The ability of systems to work together. Post-quantum migration requires compatible support across relevant wallets, applications, custodians, and infrastructure.
Cryptographic agility
The ability to adopt new cryptographic algorithms and retire vulnerable ones with limited disruption. It helps systems respond to future research and changing standards.
Key rotation
Replacing a cryptographic key. Changing a key does not necessarily change the algorithm or remove quantum vulnerability.
Rekeying
Changing the key or authorization arrangement controlling an account. On Algorand, rekeying can preserve the account’s public address while changing its spending authority.
NIST
The US National Institute of Standards and Technology. Its post-quantum program evaluates algorithms and develops standards used to guide adoption.
FIPS
Federal Information Processing Standards. These include published standards for post-quantum key establishment and digital signatures.
Algorithm selection versus standardization
Selection means an algorithm has been chosen for standards development. A published final standard is a later milestone. Selection, standardization, and validation of a particular implementation are distinct.
5. Understanding Algorand’s approach
Falcon
A lattice-based post-quantum digital signature scheme. Algorand uses a deterministic variant for State Proofs and post-quantum transaction authorisation.
Falcon-1024
The Falcon parameter set currently supported for Algorand’s native post-quantum account signatures.
Falcon-512
Another Falcon parameter set with different size and security characteristics. Algorand’s documentation identifies it as in development for launch in 2026, but not currently enabled for native account signatures.
FN-DSA
A signature scheme derived from Falcon being standardized through NIST FIPS 206. Algorand’s deterministic Falcon implementation differs from the draft FN-DSA scheme described in its documentation. However, as part of Algorand’s crypto-agile approach, it plans to also implement the NIST-approved version of Falcon once the final standard is published.
Native post-quantum account
An account whose post-quantum transaction signatures are recognized directly by the Algorand protocol.
Post-quantum signature envelope (pqsig)
The transaction structure carrying a post-quantum signature, its public key, and information identifying the signature scheme. Its design supports adding future schemes.
State Proofs
Cryptographic attestations that allow external systems to verify information about Algorand’s blockchain state. They use Falcon signatures; this protection is distinct from account and consensus signatures.
Logic Signature (LogicSig)
An Algorand transaction authorization mechanism using program logic. Falcon verification through LogicSigs enabled post-quantum account designs before native account support.
Verifiable random function (VRF)
A cryptographic function that produces randomness together with proof that it was generated correctly. The Algorand blockchain uses a VRF for committee selection during consensus. VRFs were co-invented by Silvio Micali, Algorand’s founder.
Cryptographic sortition
Algorand’s process for selecting consensus participants using verifiable randomness and stake. Cryptographic sortition was co-invented by Silvio Micali, Algorand’s founder.
Post-quantum consensus research
Work to strengthen the cryptography used in consensus messages and participant selection against quantum attacks. It is separate from deploying post-quantum account signatures.
Algorand post-quantum roadmap
The published plan for extending post-quantum capabilities across Algorand. It distinguishes deployed features, planned developments, and ongoing research; future milestones remain subject to change. Check out the roadmap here.